Nonlinear creep calculation is turned on by ticking the "Calculation of non-linear creep" checkbox in Settings of Construction stages menu.
The checks when non-linear creep is considered does not require the limit of 45 % of characteristic compressive strength (fck) for quasi-permanent combination and allow us to make an economic design. See EN 1992-1-1 art. 7.2 (3).
The nonlinear creep is calculated according to the EN 1992-1-1 art. 3.1.4 (4).